Apparatus for communication systems



Aug'. 17, 1937. L. D. WHITELOCK 2,090,088

h APPARATUS FOR COMMUNICATION SYSTEMS Filed Dec. 5,-1936 5 sheets-sheet 1 INVENTOR nelork.

% 'I /LS' ATTORNEY ams@ Ll @NN Mw?- .@lxlh y 5 Sheets-Sheet 2 Aug- 17, 1937. D. wHlTl-:LOCK

APPARATUS FOR COMMUNICATION SYSTEMS Filed Dec. 5, 1956 Aug. 17, 1937. 1 Q wHn-ELOCK 2,090,088

APPARATUS Fon COMMUNICATION SYSTEMS Filed Deo. 5, '1956 3 Sheets-Shet 3 .INVENTOR Leland D.' f z'eloclc.

BY t

HIS ATTGRNEY vPatented Aug. 17, `1937 PATENT ori-ica v APPARATUS FONGOMUNICATION SYSTEMS Leland D. Whitelock, Wilkinsburg, Pa., assigner to The Union Switch Signal Company, Swissvaie, Pa., a corporation oi.' Pennsylvania Application nei-,emper- 5, 103e.A serial No. 114,439

` 19 claims. (ci. 24e-s) I will describe two forms of apparatus embodying my invention, and will then point out the lofnovel featuresthereof in claims'.

A feature of my invention is the provision of novel and improved apparatus for communication systems wherewith an operating mechanism at one location is governed by control impulses transmitted from ay remote location, and telephone communication is effected between the two locations. Another feature of my .invention is the provision of novel and improvedapparatus for systems of the type here involved where- 0 with the operator at one location may break-in on the conversation of the operator at the other location. Still another feature of my invention is the provision of novel and improved apparatus for checking the integrity 4of the system to .insure proper operation of. the control mechanism when such operation is desired. Other features and advantages of my invention will appear as the specication progresses.'

My invention is peculiarly useful for railway train communication systems where the train brakes are to be governed at two spaced locations j on a train and telephone communication is to be effected also between the operators at the two locations. In such railway train communication systems a carrier frequency current modulated with voicefrequencies lis used for telephoning, the carrier current modulated by a single predetermined voice frequency or its equivalent is used for calling, and for brake control the carrier current coded in accordance with different brake control conditions is provided. The communica? tion channel or .transmitting vcircuit preferably includes-the track rails in the manner described and claimed in the application for United States Letters Patent Serial No. 450,135, filed May 6,

1930, by L. O. Grondahl'for Electric train signaling systems. 'I'he communication current is supplied to and received from the track rails through the medium of circuit elements electrically coupled with the trackrails, switching apparatus be ing provided at each location for effectively coupling either the receiving or the transmitting apparatus with the track rails. In such systems as heretofore proposed, the pperator actuates '55 such switching apparatus manually, especially during telephone communication, and there is no limit imposed on the length of time the equipment of a station can be held at the transmitting position. It is desirable that each operator may V break-in upon the conversation of the operator at 5 the other location in order that a message or 'signal relating to the control of the train may be delivered without delay. A v

In the accompanying drawings, Figs. 1 and 2, when taken together, constitute a diagrammatic l0 view of one form of apparatus embodying my invention when applied to a railway trainI brake control and telephone system. The apparatus o f- 1 is that to be installed on a train atthe location of the supervising operator, and which l5 location may be, for example, the locomotive of a freight train, the engineman being the rsuper- V vising operator. The apparatus of Fig. 2 isl that to be installed at another location on the train, and which location may be the caboose of a 20 freight train.` Fig. 3 is a diagrammatic, frag.- mental view of a modied form of thenapparatus of Fig. 1.

In the following description, like reference characters refer to -similar part/sin each of the 25 several views.

Although a particular application of my in vention is here' disclosed, it will be understoodV that the invention is not limited to communica- `tion systems for railway trains and is capable '30 of application in many places. This one disclosure of the invention will serve to illustrate the many places where the invention will be useful.

In certain instances, circuit controlling con@ 35 tact fingers are shown remote from the relay windings which operate them. The relationship between these elements is indicated by the fact that each such circuit controlling contact finger bears a reference character corresponding to the 40 reference character of the associated relay plus a distinctive numeral, and each such contact finger is illustrated in the position corresponding to the position of the relay.

Referring to Fig. l, the reference character EV 45 designates the usual engineers brake valve capable of assuming the usual running and brake applying positions. As shown schematically, a

circuit contact assembly is associated with, the brake valve E V by virtue of the contactsy I0 and 50 I I of the assembly being operatively connected with the brake valve handle l2. The contact I0 is adapted to make engagement with contacts Il, I5 and i6 in the lap, service and emergency D081- 'tions ofthe brake valve, respectively. The con- A 55 tact Il is adapted to make engagement with an arcuate contact I3 in al1 three of the lap, service and emergency positions of the valve. The function of this contact assembly will appear as the 5 specification progresses.

The locomotive equipment includes a coder CD. The type of coder is immaterial and may be any one of several well-known types. It is deemed sufiicient for this description to point out that when the operating `winding I'I of coder CD is energized the three code contact members 88, 40 and 50 are operated, the arrangement being such that contact member 30 engages a front contact I8 at the rate of 30 times per minute, the coni5 tact member 40 engages a front contact I8 at the -ratte of 40 times per minute, and the contact member 50 engages a front contact 20 at the rate of 50 times per minute. It will be understood that my invention is not limited to these specific rates of operation of the coder contacts and that other rates may be selected if desired. A relay CX is associated with coder CD for governing the operation thereof. Relay CX is controlled over a circuit that extends from the B terminal of any convenient source of current such asabattery not shown, winding of relay CX, contact II--I3'of the contact assembly, wire 2I,-back contact 22 of a relay TZ to be referred to later, and thence to the C terminal of the same source of current. I'he energizing circuit for the coder CD includes battery terminal B, front contact`23 `of relay CX, 'winding I1 of coder CD, contact II-I3, wire 2|, back contact 22 and to the C battery terminal. It follows that with the brake valve EV operated to a running position the relay .CX is deenergized and the coder CD is inactive, but that operation of the brake valve EVtto a brake applying position causes the relay CX to be energized and the coder CD to be active. The 40 manner whereby the code contacts 30, 40 and 50 are effective to ,establish different brake control codes will appear when the operation of the system is described.

The transmitting apparatus on the locomotive includes an oscillator OSI, a microphone M, a modulator -M.D, a band pass filter BPF, and a power amplifier PA, as well as control and send- 00 phone conversationv is not being carried on, is

preferably carried on a rack or a hook notshown and has attached thereto a handle 85 to facilitate its being brought close to the person speaking. Two contacts 86 and 81 are operatively connected .with the microphone as indicated by a dotted line, the arrangement being such that contacts 88 and 61 occupy the positions illustrated by solid lines when the microphone is placed on the hook and are operated to the positions indicated by dotted lines when the microphone is lifted off the hook. The microphone M is connected over wires 29 and- 3l with the modulator MD to eect modulation of the carrier supplied from the oscillator OSI by the voice frequencies produced by speaking into the microphone. 'Ihe side band frequencies resulting from such modulation are supplied to the input side of the band pass filter BPF over wires 32 and 33. the carrier being suppressed by the balanced arrangement of the circuits of the modulator. The filter BPF is proportioned and adjusted to suppress one side band and to pass the other. To assist in vunderstanding my invention, I shall assume that the lower side band is suppressed and the upper side band is passed, it being understood, of course, that the upper side band may be suppressed and the lower side band passed if desired. The output side of the filter BPF is connected with the input terminals of the power amplifier PA over wires 34 and 35. For reasons to appear hereinafter, the wires 32 and 35 are preferably grounded as shown at 86 and 81, respectively, and the wires 33 and 34 are connected over a front .contact 9 of a relay AX. Thus, the -output of the modulator MD is ordinarily passed to the power amplifier through the band pass filter BPF, but at such times as the relay AX is energized and its front contact 8 closed the output of the modulator is bypassed around the filter to the power amplifier.

The power ampliiiervPA' may be any one of several types such as, for example, two power electron tubes connected in the push-pull arrangement. Hence, the carrier current supplied to the input terminals of power amplifier PA is supplied to a sending circuit and inv turn to a transmitting circuit amplied to a relatively high energy level. In this instance, the sending circuit may be traced-from the lower right-hand terminal of amplifier PA over wire 38, rear truck wheels 31, track rails 38, forward truck wheels 89, and wire 4I to the upper right-hand terminal of the power amplifier. Currentthus supplied to the track rails which form a part of the-transmitting circuitproduces an electromotive force therein, which in turn causes current to flow in the rails in both directions from the locomotive in the well-known manner. The oscillator OSI,

` modulator MD, filter BPF and power amplifier PA are shown conventionally in order to simplify the drawings as much as possible, since the spe' electrodes 88 and 88. 'I'he relays CR and AX govern the oscillating circuit associated with oscillator OSI, the relay CR.` completing at its `back contact 43 a connection by which the condenser 28 is interposed in the circuit, and the relay AX completing at its back contact 44 a connection by which the condenser 25 is interposed in the circuit. The relay CR also governs the connection of the modulator MD. With relay CR released, closing its back contact A51, a connection is completed from the modulator MD by which a balanced arrangement of the circuits thereof is effected, but when relay CR'is picked up, closing its front contact 58, the connection for the modulator is shifted so that a parallel arrangement of its circuits is effected. Relay AX also controls at front contact the bypass around the filter BPF describen hereinbefore.

These three i'ela.ys"y PRVCR and AX are themselves governed over a circuit network. A push button PBI when operated to close a contact 45-46 completes a circuit extending from the B terminal over back contact' ICX of the relay CX,

contact 45-46, wire 41, winding of relay PR and to the C terminal, and the relay PRis energized. Operation of a push button PB2 completes a circuit extending from the B lbattery terminal over back contact ICX, contact 48-49 of push button PB2, wire 5I, windings of relays CR and PR in series and to the C terminal, and the'two relays CR and PR are energized in series. Operation of a push button PB3 completes a circuitextending from the B terminal over back contact ICX, contact 52-53 of push button PBS, wire 54, windings of relays AX, CR and PR in series and to the C terminal, and the 'three relays are energized in series. The three control relays may also be energized in series by means of another circuit that extends from B terminal over front contact 55 of a relay TR, wires 55 and 54, the windings of the three relays in series, and to the C terminal. Again, these three relays may be energized over B terminal, front contact I2I of relay CX, wires 55 and 54, windings of the relays in series, and to the C terminal. Operation of either push button PBI or PB2 also completes a circuit easily traced by which a relay |24, to be referred to later, is energized, the circuit including contact, I35-I31 of push button PBI or contact I38I3`9 of push button PB2.

Operation oi' the push button PBI to energize relay PR. leaving the two relaysAX and CR deenergized, establishes the telephone condition for the transmitting apparatus. Under this telephone condition the oscillator OSI and modulator MD are rendered active, the frequency 'of the carrier delivered by the oscillator being determined by the three condensers 24, 25 and 26 in 40 parallel, and the modulator MD being in its balanced arrangement. To better illustrate my invention, I shall assume that the frequency of the carrier current when the three condensers 24, 25 and,25 are in circuit is 7000 cycles per second. Taking the voice frequency range to extend from 600 to 2000 cycles per second, the addition and subtraction of the voice frequencies with the carrier of '1000 cycles produces an upper side band extending from '7600 to 9000 cycles and a lower side band extending from 6400 to 5000 cycles. As-

suming the'band pass filter BPF to be proportioned'to pass the upper side band only, it is clear that operating the push button PBI and speaking into the microphone M is eective to causev a carrier telephone current to be supplied tothe track rails of the transmitting circuit, the current flowing in the track rails in both directions from the locomotive. .Operation of push'button PB2 to pick up `relays CR and PR leaving relay AX deenergized, establishes the calling condition of the transmitting apparatus. 'I'his setup of the lcontrolrelays is eifective to'render the oscillator OSI and the modulator MID active, the modulator being now in its parallel arrangement and the frequency of the carrier generated by oscillator OSI being determined by the two condensers 24 and 25, I shall assume that the frequency oi' the calling current is 8050 cycles, that is, it is the equivalent of the original carrier of 7000 cycles modulated by a voice frequency of 1050 cycles. The modulator MD being now in its parallel arrangement, the current of 8050 cycles is deliv- '750 ered through the modulator MD and the band cillating circuit now delivers a carrier current of a frequency higher than the upper side band of the telephone current referred to hereinbefore. For example, the carrier current now delivered by the oscillator OSI may have a frequency of 13,000 cycles per second. Since the picking up of relay AX completes the bypass around the filter BPF, this break-in carrier current of 13,000 cycles is delivered through modulator MD to the power amplifier PA with little attenuation and is then in turn supplied to the track rails. Since the circuit for energizing the three relays AX, CR and PR in series is Lcompleted at the front contact 55 of relay TR and also at the front contact I2I of-relay CX, it follows that an impulse of current of 13,000 cycles is delivered to the track rails when either of the relays TR or CX is energized. As will appear hereinafter, impulses of current of 13,000 cycles are supplied to the trackrails by virtue of operation oi' the relays TR and CX for providing check impulses. and spectively. A

The locomotive receiving apparatus preferably includes an inductor coil CC, two band pass fllbrake control impulses, re-

ters FI and F2, an amplifier demodulator AD,

an oscillator OS2, an audio amplifier AM, aloud speaker LS and a check circuit SC. The ampliiierdeniodulator AD, oscillator OS2 and audio. amplier 4AM are each shown conventionally only for the sake of simplicity since each of these devices may take any one of several wellknown forms and thespecific structure thereof is not a part of the present invention.

The inductor coil CC is preferably of the air with thelinput terminals of the amplifier demodulator AD. Carrier current is supplied to the amplifier demodulat'or AD for mixing with the incoming carrier current iby theoscillator OS2 and the output terminals of the dernodulator` A D are connected with the input side of the filter F2, the output side of which filter is connected with the input terminals of the amplier AM.` 'Ihe loud speaker LS and the check circuit SC are connected with the output terminalsd'of amplifier-AM in parallel', the connection to the loud speaker Aincluding wires 'I0.and 1I. The check circuit SC includes a, condenser 6I, reactor 62 ,and the contact 61 operated by, the microphone M. A portion of the reactor 62 is connected with the input terminalsof a rectifier A63,

lthe output terminals of which are connected with 'the operating vwinding of ajrelay 54.

eating and checking apparatuswhich consists of a SC, since the check both directions, the filter FI is proportioned to' pass a band of frequencies extending'from '1600 to 9000 cycles and the oscillator OS2 is effective to supply a carrier of 7000 cycles. 'I'he filter F2 is proportioned to pass a band of frequencies extending from 600 to 2000 cycles and the check circuit SC is proportioned to be sharply tuned at 1050 cycles. Hence, a carrier telephone current of the range of '1600 to 9000 cycles flowing inthe track .rails at the locomotive induces an electromotive force in the coil CC which is passed by the illterFI and demodulated at the ampliiler demodulator AD, producing in the output of the demodulator voicel frequencies of a. range of 600 to 2000 cycles and other products of demodulation. The filter F2 is effective to pass this range of voice frequencies and suppress the other products of demodulation. The voice frequencies passed by lter F2 and amplified at the amplifier AM and reproduced by the loud speaker LS, the check circuit SC being non-responsive,

since the energy 'of the telephone current corresponding to the frequency to which the check circuit is responsive is negligible. In the event a calling current of 8050 cycles flows in the track rails an electromotive force is induced in the coil CC which is passed by the filter FI and demodulated to produce a frequency of 1050 cycles in the output of the demodulator. 'I'his frequency is passed by filter F2 and amplified by the amplifier AM and is effective to produce a note at the loudspeaker and to energize the relay 64through the medium of the'check circuit circuit is sharply tuned at this frequency of 1050 cycles.

The locomotive is also equipped with indigroup of relays IX, 2X, TR, TX and TZ, and an indicator lamp L. The relay terminal over front contact 12 of relay 84, wire 13, winding of relay IX, back contact 22 of relay TZ and to the C terminal. The relay 2X is energized over a circuit including terminal B, winding ofl relay 2X, front contact 14 of relay IX, back contact 22 and to the C battery terminal. The lamp circuit includes the front contact 15 of relay 2X, the lamp L, wire 2|, and the back contact 22 of relay TZ. The relay IX is of the l ordinary acting type but the relay 2X is slowI releasing in character. Relays 'IR and 'IXcomprise a timing means and are operated 'in par allel being energized over a circuit including B battery terminal, windings of the two relays TR and'TX in parallel, back contact 16 of relay CX, back contact 11 of relay IX, wire 18, contact 6B of the microphone, wires 19 and 2l, back contact 22 of relay TZ and to the C terminal. The relay TR controls the three relays CR, PR and AX in the manner described hereinhefore, and the relay TX controls the relay TZ, the pickup circuit for relay 'I'Z being completed at the front contact 89 ofthe relay TX. Relay TZ is- IX is.controlled by means of a circuit extending from B battery MD, a lter BPF and a power amplier PA,

and each of which devices is similar to the corresponding device of the locomotive equipment. The transmitting apparatus on the caboose is governed by two relays PR and CR, similar to the corresponding relays of Fig. 1, and which relays are also controlled in a similar manner, the relay PR being energized alone when a push button PB4 is operated and the two relays CR and PR being energized' in series when a push button PB5 is operated. The two relays PR and CR of Fig. 2 may also be energized in series over a front contact 93 of a relay 84 to be referred to later. The relay PR controls at its front contact a supply of plate voltage for the tubes of the `oscillator OSI and of the modulator MD. 'Ihe relay CR governs the oscillating circuit and the connections for the'modulator. With relay 'CR released, closing its back contacts 90 and 93,

the condenser 92 is interposed in the oscillating circuit and the circuits of the modulator MD are arranged in a balanced arrangement. When relay CR is energized opening back contacts 90 and 93, and closing front contact 94, the condenser 92 is disconnected from the oscillating circuit and the modulator vcircuits are'switched toa parallel arrangement. The output terminals of the power amplifier PA of Fig. 2 are connected with a sending circuit that includes the truck wheels 95 and 98 at the opposite ends of the caboose, and hence are directly coupled with the track rails of the transmitting circuit. To agree with the previously assumed frequencies for the apparatus on the locomotive, the caboose oscillator OSI is adjusted to generate a carrier frequency of '7000 cycles when the two condensers 9| and 92 are interposed inthe associated oscillating circuit and to generate a carrier frequency of 8050 cycles when the condenser 9I alone is included in the oscillating circuit.

AIt is clear that operating the push button PB4 and speaking into the microphone M is effective to supply to the track rails a carrier telephone is effective to supply a current of 8050 cycles to the track rails, and which latter current is utilized as a return check impulse in a manner shortly to appear.

The caboose is provided with receiving apparatus similar to the receiving apparatus of Fig. 1 except that an input transformer TI, an auxiliary inductor coil BC, a frequency conversion unit designated as a whole by the reference character FC, andbrake control equipment are added.

The inductor coil CC of Fig. 2 is preferably mounted on the caboose roof on a vertical plane to be in inductive relation with the track rails and is interposed in a receiving circuit including back contact 2PR of relay PR, the upper portion of the primary winding 91 of transformer TI 'and condenser 98. This receiving circuit is tuned to efficiently pass a current having a range of frequencies extending from 7600 to 9000 cycles. A

The output of the amplifier AM of Fig. 2 is delivered to the loud speaker LS, a check circuit SCI and a brake control circuit BCC in parallel. The check circuit SCI includes a, condenser II3, 'a reactor II4 and a contact II5 operated by the microphone M, a portion of reactor II4 'being connected with the winding of relay 39 magnets LM, SM and EM maybe used to'govaooopss..

'u through rect-mer Ht. This cheek circuit SCI is tuned sharply to respond to` a current of 1000 cycles whereas the ch'eck circuit on the locomotive is tuned'to respond to a current of a frequency of 1050 cycles. The brake control circuit BCC includes a reactor H9, a condenser |20, and the input side of a rectifier H0, the output terminals of rectifier ||9 being connected with three code selectors S30. S40 and S50 in parallel. This brake control circuit is proportioned to respond to a current of 1000 cycles. The code selectors S30, S40 and S50 may be any one of several different types and itis deemed suillcientto point out that selector S is responsive onlyto a current interrupted or coded at the rate of 30 times per minute,` the selector S is responsive only to current coded at the rate of 40 times, per minute, and the selector S50 is responsive to current coded at the rate of 50 times per minute. Brake controlling ma/gnets LM, SM and EM are connected -with the selectors S30, S40 and S50, respectively. It follows that magnet LM is energized when a current of 1000 cycles coded at thev rate of 30 times per minute appears in the output of. the amplifier AM, magnet SM is energized when such current is 4coded at the rate of 40 times per minute and magnet EM is energized when the current is coded at the rate of 50 times per minute. The

ern electropneumatic brake valves not shown in the usual manner or they may' be employed to govern an indicator for indicating to an operator the manner in whichvhe is to operate a l manually operated brake controlling valve. To

check the position ofl thev brake controlling apparatus the magnets LM, SM and EM are provided with back contacts |20, |29 and |30, re-

spectively. t

The auxiliary inductor coilr BC is preferably mounted on the caboose roof in inductive rela-,

tion with the track rails and Vhence with the transmitting circuit, and is connected to the frequency conversion unit FC, the immediate circuit extending from the lower terminal of coil BC over wire 99, a portion of winding |00 of a transformer T3, condenser |0| and wire |02 back to the opposite terminal of coil BC. This circuit is tuned to elciently pass a carrier current having a frequency of 13,000 cycles.A That is, the auxiliary coil BC is effective to receive the breakin and break control current supplied by the 'transmitting apparatus of the locomotive. The

winding |00 of transformer T3 is interposed in a connection between a. control grid |05 and thel cathode element '|08 of an electron tube |03, the

connection being completed through the ground electrodes i|04 and An oscillator OS3 is connected between a second control grid |01 and the cathode element |00 of tube |03, while the plate circuit of the tube includes the primary winding |09 of a coupling transformer T2.

To agree with the frequency of 13,000 cycles to be received by the auxiliary inductor coil BC,

the oscillator OSS of the frequency conversion unit would preferably deliver a carrier currentl of 5000 cycles. The product of mixing the local carrier of 5000 cycles with the incoming current. of 13,000 cycles is the addition and subtraction frequencies, namely, 18,000 cycles and 8000 cycles. That is, frequencies of 18,000 and 8000 cycles are caused to appear in 'the plate circuit 'of tube |03 in response to a current of 13,000 cycles received by the inductor coil BC. and these lfrequencies in the plate circuit are effective to induce'i anl elec- I tromotive` force of corresponding frequencies in the secondary winding ||0 of the coupling transformer T2. The secondary' winding ||0 is connected with the lower portion of the primary vwinrling 91 of transformer TI over a simple4 circuit easily traced, a condenser being associated with this circuit to tune the circuibto maximum efficiency at 8000 cycles and thereby partially eliminate the other components of the frequency conversion. Hence, as a result of the frequency conversion, an electromotive force of 8000 'cycles is induced in the secondary winding ||2 of transformer TI and is applied to the inputside of the illter FI. Since'8000 cycles falls within the pass band of the filter FI (7600 to 9000), this current is passed to the demodulator where it is mixed with the local frequencies of '7000.cycles supplied by the oscillator OS2, with f the result that current of4 1000 cycles appears in the output o the demodulator. Since 1000 cycles falls within the pass\band of the lter F2 (600 to 2000), this current is passed to the amplifier AM and is effective to operate the relay 84 of the check Acircuit SCI and to effectively energize .the brake controlling circuit BCC, aswell as to' sound a corresponding note at the loud ving sounded at the loud speaker. 'Electromotive force induced in the auxiliary coil BC in response to the current of 13,000 cycles flowing in the transmitting circuit when applied to the frequency conversion unit FC and then in turn to the receiving apparatus results in effectively iniluencingv the check circuit and the brake control circuit, as well as sounding a corresponding note at the loud speaker.

In describing the operation of the apparatus of Figs. 1 and 2, I shall first consider 4the operations that take place in exchanging check impulses between the locomotive and the caboose when the engineers brake valve EV is set at a running position and the two microphones M are both placed on `|their respective hooks. At the start the timing relays TR and TX and the relay IX, as well as the relay CX are down. Current is now supplied to the timing relays TR and 'IX over the back contacts 11 and 16 of relays IX and CX, respectively, and the timing relays are Vset into operation. Therelay TR shortly picks up, closing front contact 55, since the pickup period of relay TR. is `of theorder of 5 seconds, whereas the pickup period of relay TX is of the order of 1 minute. With relay TR picked up, the control relays AX,'CR andPR are energized in series, with the result that the transmitting apparatus is rendered active to supply a current of 13,000 cycles to the track rails, and which current forms an 'outgoing check impulse that remains in effect until a return check impulse is received at the locomotive. The A13,000 cycle current induces an electromotive force in vthe auxiliary inductor coil B C at the caboose, which electromotive force when passed by the frequency conversion .unit FC and applied to the receiving apparatus on the caboose produces a current of 1000 cycles inthe output. of the associated amplifier AM. As a result of this current of 1000 cycles the relay. 84 is energized and picks up closing itsfront contact 83 after a slight slow pickup period,l and the loud speaker LS sounds a corresponding note, the brakel control magnets LM, ySM and EM being non-responsive to the current since the current is not coded. The relay 84 on picking up energizes the associated control relays CR and PR, with the result that d yelectromotive force in the locomotive coil CC,

which electromotive force when applied to the locomotive receiving apparatus appears in the output of the associated amplifier AM as a current of 1050 cycles, with the result that the relay 64 is energized and a corresponding signal is sounded by the loud speaker. Relay 8l when picked up to close front contact 12 causes relay IX and in turn the relay 2X to be energized. Relay 2X on picking up completes the circuit for the lamp L and the lamp is now illuminated to indicate to the engineman that the apparatus is in operating order. When relay IX picks up to open back contact 11 the timing relays TR and TX are deenergized and restored to their initial positions,. the relay TR being slightly slow releasing in character. When relay TR. releases,

. the associated control relays AX, CR and PR.

are deenergized and the outgoing check impulse ceases. With the discontinuing of the outgoing check impulse the relay 84 of thecaboose apparatus is deenergized and releases to discontinue the return check impulse, with the result that the relay IX on the locomotive is at once deenergized. 'I'he relay 2X, however, remains picked up since it is slow releasing in character and the lamp L remains illuminated. With the release of relay IX the circuit for the timing relays 'IR and 'IX is again closed and the operation is repeated. It follows that the apparatus automatically exchanges impulses between the locomotive and the caboose once for each operating period of the timing relay TR. 'I'he relay 2X is provided with a release period that is somewhat greater -than the operating period of relay TR and hence remains picked up from one check impulse to the next, and the lamp L is continuously illuminatedas long as the check impulses are periodically exchanged.

Since therelay 'I'X is reset at each exchange of impulses it is not operated to close its contact as long as the system is in proper operating order. In the event of `a failure in the apparatus and no check impulse is received at the locomotive, the operation of the relay TX is continued and at the end of one minute closes the contact 80' and energizes the relay T Z, which relay is then retained energized over its stick circuit. With relay TZ picked up connection with the C terminal of the current source is broken at the back contact 22 and current is removed from the brake controlling equipment, the lamp L be.- ing now dark to indicate to the engineman that the brake controlling equipment is out of order. It is to be noted'that if the fault is 'of short duration and the check impulses are reestablished the lamp L is again illuminated and the operation of exchanging check impulses is reestablished. However, when the fault is of a relatively long period, that is, a period equal to the operating time of the relay TX, the apparatus is automatically cut out of service through the medium of the relay TZ. Should the engineman desire to reestablish the operation of the apparatus after it has once been cut out through the medium of relay TZ, he can do so by operating the push button 82.

Assuming now the check impulses are being exchanged in the manner recited above and the engineman makes a brake application by operating the brake valve EV to the service position closing contacts Ill-I5 and I I-I3, the relay CX is at once picked up closing front contact 23 to start operation of the coder CD, opening back contact 'I8 to discontinue the operation of the timing relays, land closing front contact I2I to energize the control relays. Under these circums'tances, the transmitting apparatus on the locomotiveis rendered active to supply a current of 13,000 cycles. Each time the code contact I9-40fis closed a shunt path is completed for the oscillating circuit of oscillator OSI and the generated carrier current is interrupted or coded. This shunt path includes wire I22 connected to the upper right-hand terminal of the oscillating circuit, contact III-I5, code contact I9-40 and wire |23 to the lower right-'hand terminal of the oscillating circuit. It follows thatthe outgoing current of 13,000 cycles is interrupted or coded at the coded rate oi 40 times per minute as long as the brake valve EV is retained at the service position.

'I'he electromotive force now induced in the inductor coil BC at the caboose, after being con'- verted by the frequency conversion unit FC and applied to the receiving apparatus, produces in the output of the amplier AM a current of 1000 cycles coded at the rate of 40 times per minute, with the result that the brake magnet SM is energized. It is to be pointed out that the relay 84 does not respond to this coding current since its circuit is broken by the back contactv |29 of magnet SM and the relay 84 is slightly slow to pick up in character. It is clear that operation of-the brake valve EV to either the lap position or the emergency position causes a similar operation of the apparatus except for the fact that the outgoing current is -coded at the rate of 30 or 50 times per minute and either the brake controlling magnet LM or EM is selected. Restoring the brake valve EV to the running `position deenergizes the relay CX and the operation of automatically exchanging check impulses is reestablished. l

' In the event the engineman desires to initiate telephone communication, he would ilrst remove his microphone from the hook, opening contacts 66 and 31 and thereby discontinuing the check impulses. The engineman would next operate the push button FB2 to pick up the relays CR and PR and set the transmitting apparatus in a condition for 'supplying to the track rails a calling current of 8050 cycles, the current continuing uninterrupted as long as the push button PB2 is operated. Since the relay I24A is also energized in response to operation of the push button PB! the locomotive receiving circuit is held openand' made non-responsive to the outgoing calling current. 'I'he electromotive force induced in the inductor coil CC on the caboose in response to this calling. current, when applied to the associated receiving apparatus, produces a kcurrent of 1050 cycles in the output of the amplifier AM, with thev result that acorresponding signal is sounded at the loud speaker. However, neither the check After a suitable interval the engineman'would rel lease his push button PB! and discontinue the callingv current. 'I'he caboose operator would now respond by operating his push button PBl and speaking the usual hello signal in the microphone. Fro'm this point on, telephone conversation would be carried on by the proper operation of the push buttons PBI and PBI, each operator moving his push button when he wishes to speak and releasing his push button whenhe wishes to receive.

If the operator at the caboose desires to initiate telephone communication, he would "remove hismicrophone from the hook, opening contact I I5 in the check'circuit and thereby discontinue the return check `impulses. 'I'he caboose operator would then operate his push button PB! to pick up the relays CR and PR and render the caboose transmitting apparatus active to supply a calling current of 8050 cycles. The electromotive force induced in the Inductor coil CC on the locomotive in response to this calling current is effective to produce after demodulation a current of '1050 cycles in the output of'the amplifier AM. which current creates acorresponding signal Vat the loud speaker LS and energizes the relay 84 of the check circuit. Relay B4 in turn causes the .relay IX to be energized, which relay .on picking up renders the locomotive apparatus inactive to further continue the supply of check impulses. 'I'he prolonged signal at the loud 40 speaker LS on the locomotive would indicate to 'the engineman that telephone communication is desired and he would at once remove his microphone from the hook ready to telephone. After a suitable period the operator in the caboose would release the push button PBii and discontinue the calling current. Fromj this point on, telephone conversation would be effected in the l same manner as before'described.

In the event the engineman desires to break in on the conversation of the caboose operator, theengineman would operate the push button PBS and send out from the locomotive a current of13,000 cycles. Although the caboose apparatus is now in a-transmitting condition. the electromotive force induced in the, auxiliary inductor coil BC in response to the 13,000 cycle current would be converted by the frequency conversion unit FC and applied to the receiving` apparatus and produce a non-'coded current of 1000 cycles in the output of the anplifier AM. Such a signal at the loud speaker LS would indicate to the caboose operator that the engineman desired to break in upon his conversation and he would setv his apparatus in a receiving condition. In the 65 event an emergencyvarose during ythe telephone conversation of thecaboose operator that relquired. an application of, the train'brakes, the engineman would operate his brake valve to the desired position with the resu1tthat the locoy70 motive apparatus would send out control impulses of 13,000 cycles coded according to the position of the brake valve. I'his current of 13,000 cycles would be received by the caboose inductor 'coil BC and would be effective to energize the 75 corresponding brake magnet. notwithstanding the fact that the caboose operator is transmitting a telephone conversation at the same time.

' It is to be pointed out that the inductor coil BC would be little influenced by the usual telephone current of the frequencies of '1600 to 9000 cyclesbecause of the tuning of the circuit to which it is connected. The small portion of '7600 to 9000 cycle current that is induced in the coil BC and hence applied to the frequency con- -version unit would cause no interference in the receiving apparatus as the lower products of frequency conversion would be 2600 to 4000 cycles and these frequencies would be cut of! at the filter FI since they are outside ofthe pass band of that filter. The higher products of frequencyconversion would be 12,600 t'o 14,000 cycles and *v this band of frequencies is also outside of the pass band of the filter FI. V

In Fig. 3 a modication of the timing means of Fig. l is disclosed. In this modification the relay TX of Fig. 1 is omitted and the relay TZ is re- 'placed by a relay 'IZI which is slow releasing in 'character'. .The operating winding of relay TZI is interposed in the circuit for the indication vlamp jL and hence the relay is energized and picked up as long as the relay 2X is picked up. As set forth in describing the apparatus of Fig. l, relay 2X is provided with a release period that is greater than the time interval between two successive check impulses and remains picked up as long as the check impulses are properly received. The connection to the C terminal of the current source for the brakecontrol apparatus is completed at the front contact I3I of relay TZI. It follows that as long as the check impulses are properly exchanged between the locomotive and the caboose and the relay 2X is vpicked up, the relay 'IZI is picked up andv the control apparatus is operative, but thgt failure to receivel a check impulse which causes the relay 2X to rei lease will in turn deenergize relay 'IZI and that relay will release at the expiration of its slow release period and render the control apparatus inoperative by opening the circuit connection to the terminal C ofthe current source. In Fig. 3 a manually operated push button |33 is provided for initially energizing relay 'IZ I and thereby initially setting the apparatus into operation for exchanging'check impulses. It is clear that with the locomotive equipment modified as disclosed i'n Fig. 3 the operation of the system is essentially the same as' described hereinbefore. v Although I have-herein shownI and described only two forms of apparatus embodying my invention, it is understood that various changes and modifications may be-made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus ,described my invention, what I claim is:

l. In `apparatus for communicating between two spaced locations over a single transmitting circuit the combination comprising receiving apparatus at one location coupled with the circuit and effectively responsive to communication current of a predetermined frequency range, an auxiliary receiving means at /said one location including Aa conductor coupled with the circuit i apparatus to establish a signal peculiar to said signaling current.

2. In apparatus for telephone communication between two spaced locations over a single transmitting circuit the combination comprising re- CFI ceiving apparatus at one location coupled with' the circuit and .effective to demodulate and reproduce at a loud speaker the voice frequencies of a selected side band of a given carrier modulated by voice frequencies, an auxiliary receiving means at said one location including a conductor coupled with the circuit and a frequency conversion unit capable of converting a signaling current of a given frequency outside of said 5 side band to a current of a desired frequency within said side band, 4and circuit means to couple the output side of said conversion unit with the input side of said lreceiving apparatus to establish a peculiar note at the loud speaker 0 in response to such signaling current flowing in the transmitting circuit.

3. In apparatus for telephone communication between two spaced locations over a single transmitting circuit the combination comprising receiving apparatus at one location coupled with the circuit and effective to demodulate and reproduce at a loud speaker the voice frequencies of a selected side band of a given carrier modulated by voice frequencies, a frequency conversion unit at said one location and including an electron tube and a source of carrier current connected to one control grid of the tube, said unit effective to mix current from said source with a signaling current of a given frequency l outside of said side band to convert the given frequency to a desired frequency within said side band, a first circuit means connected to another control grid of said electron tube and having a conductor coupled with the transmitting circuit, said flrst circuit means being tuned sharply at said given frequency, and a second circuit means to couple the plate circuit of said tube with the input side of the receiving apparatus and tuned to effectively pass said desired'freg', quency whereby a peculiar note is sounded at the loud speaker in response to a signaling current of said given frequency owing in the transmitting circuit.

4. In apparatus for communicating between 0 two spaced locations over a single transmitting circuit the 'combination comprising equipment at each location each of which equipments includes transmitting apparatus capable of supplyng to said circuit communication current of a predetermined frequency .range and receiving apparatus effectively influenced by current of said frequency range flowing in said circuit, auxiliary receiving means at one of the locations including'a conductor coupled with the 60 circuit and a frequency conversion unit eective to convert a signaling current of a frequency outside of said predetermined frequency range to a current of a frequency within said range, circuit means to couple said conversion G5 unit with the receiving apparatus to establish 75 plying to said circuit communication current of a predetermined frequency range and receiving apparatus effectively influenced by current of said frequency range -flowing in said circuit, auxiliary receiving means at one of the locations including a conductor coupled with the circuit and a frequency conversion unit effective to convert a signaling .current of a frequency outside of said predetermined frequency rangev to a current of a frequency within said range, circuit means to couple said conversion unit with the receiving apparatus to establish a signal peculiar to said lsignaling current, and means at the other location to cooperate with the transmitting apparatus at said other location in supplying at times such signaling current to the transmitting circuit.

6. In apparatus for communicating between two spaced locations over a single transmitting circuit the combination comprising vequipment -at each location each of which equipments invkcludes transmitting apparatus capable of supplying to -said circuit communication current of` a predetermined frequency range and receiving apparatus effectively inuenced by current of said vfrequency range flowing in said circuit, switching means at each location to effectively couple either the transmitting apparatus or the receiving apparatus at the same location to said circuit, auxiliary receiving means at one of said locations including a conductor coupled to the circuit and a frequency conversion unit eiective to convert a signaling current of Aa frequency outside ofsaid predetermined frequency range to a current of a frequency within said range, circuit means to couple said conversion unit with the receiving apparatus to establish irrespectiveof .the position of the associated switching means ,a signal peculiar to said sigtransmitting apparatus capable of supplying a f selected side band of a given carrier current modulated by voice frequencies and receiving apparatus capable of demodulating such selected side band and reproducing the voice frequencies, switching apparatus at each location each operable to different positions to couple either the transmitting apparatus or the receiving apparatus to said circuit, auxiliary receiving means at one location including a conductor coupled with the circuit and a frequency conversion unit op- 'erable to convert a signaling current having a vfrequency' outside of said selected side band to a predetermined frequency within said side band, circuit means to couple the conversionl unit to the receiving apparatus to produce irrespective of the position of the switching apparatus at said one location a note peculiar to the signaling current, and means at'the other location to cooperate with the transmitting apparatus to superable to different positions to couple either the'v transmitting apparatus or the receiving apparatus to said circuit, and break-in apparatus consisting of means at one location to cooperate with the transmitting apparatus to supply to the circuit signaling current of a frequency outside of said selected side band and a frequency conversion unit at the other location having its input side coupled with the circuit and its output side coupled with the receiving apparatus, said unit being operable to convert said signaling current to a current having a predetermined frequency within said side band 9. In apparatus for telephoning between two spaced locations over a single transmitting circuit the combination comprising equipment at.

each location each of which equipments includes transmitting apparatus capable of supplying a selected side band of a given carrier current modulated by voice frequencies and receiving apparatus capable of demodulating such selected side band and reproducing the voice frequencies, switching apparatus at each location each operable to different positions to couple either the transmitting apparatus or the receiving apparatus to said circuit, and break-in apparatus consisting of means at one location to cooperate with the transmitting apparatus to supply to the circuit signaling current of a frequency outside 'of said selected side band and a frequency conversion unit at the other location and which unit includes an relectron tube having its plate circuit coupled with the receiving apparatus, one control grid circuit coupled with the transmitting circuit land a second control grid connected with an oscillator supplying a carrier current which carrier when mixed with the signaling current produces a predetermined frequency within said side band.

10. In apparatus-for telephoning between two 'spaced locations over a single transmitting circuit the combination comprising equipmentat each location each of which equipments includes transmitting apparatus effective to supply the upper side band of a given carrier current modulated with voice frequencies and receiving apparatus effective to demodulate such upper side band and reproduce the voice frequencies. and break-in apparatus consisting of means at one location for supplying to the transmitting circuit a current having a predetermined frequency above said upper side band and a frequency conversion unit at the other location including a source of carrier current which when mixed with said predetermined frequency produces a desired frequency within said upper side band, said unit having its input side coupled with the transmitting circuit and its output side coupled with the input side of the receiving apparatus.

11. In apparatus for telephoning between two spaced locations on a railway train the combination comprising equipment at each location each of which equipments includes' transmitting apparatus capable of supplying a selected side band of a given carrier current modulated with voice frequencies and receiving apparatus effective to demodulate such selected side band vand reproduce the voice frequencies, manually operable switching means at each location to selectively couple either the transmitting apparatus or the receiving apparatus to the track rails, and breakin apparatus consisting of means at one location for supplying to the rails a current of a predetermined frequency outside of said selected side band and a frequency conversion unit at the other location operable to convert said predetermined frequency to a desired frequency within said side band, said unit having its input side coupledvwith the track rails through a circuit tuned at said predetermined frequency and its output side coupled with the receiving apparatus through a circuit tuned at said desired frequency.

12. In apparatus for communicating between two spaced locations over a single transmitting circuit the combination comprising transmitting apparatus at one location coupled with the circuit, said apparatus having a telephone condition in which' it is effective to supply a selected side band of a given carrier modulated at voice frequencies and a control condition in which it is effective to supply a current of a predetermined frequency outside of said side band coded at different control codes in accordance with different positions of a control member, receiving apparatus at the other location operable to demodulate said selected side band, a loud speaker and a control circuit network connected in parallel to the output terminals of the receiving apparatus, said -network selectively responsive to a desired voice frequency'when coded in accordance with said control codes, a frequency conversion unit at said other location effective to convert said predetermined frequency to a frequency within said side band and which frequency is equal to said cary rier modulated by said desired voice frequency,

speaker and a control circuit network connectedl in parallel with the output terminals of said receiving apparatus, said control network selectively responsive to a given voice frequency when coded at different control codes, a frequency conversion unit including a source of carrier current and an electron tube the plate circuit of which is coupled with the input of the receiving apparatus, said unit effective to mix current from said source with a control current of a predetermined frequency outside vof said side band to convert said predetermined frequency to a frequency Within the side band and which latter frequency is equal to said given carrier modulated by said given voice frequency, a rst receiving circuittuned to effectively pass said side band and connected with the input of the receiving apparatus for receiving a telephone current, and a second receiving circuit tuned sharply at said predetermined fre- -quency and connected with the input of said conversion unit for controlling said control network by coded control current.

14. Inl apparatus for communicating between -two spaced locations the combination comprising,

control apparatus partly at each of said locations and effective to cause an operating mechanism at one location to register with different positions of a control member at the other location,

checking means partly at each location to cause said control apparatus to exchange between the t and operative a given period after the device 5 mechanism at one location to register with difdetermined time interval to initiate the sending of a check impulse and to maintain the sending of such impulse until the receipt of a return check impulse from said one location, and means controlled by each suchA return impulse to initiate a new operation of the timing device. Y

15. In apparatus for communicating between two spaced locations the combination comprising, control apparatus partly at'eaclr of said locations of a, cheek impulse, said second relay having a and effective to cause an Operating mechanism relatively long pickup period and effective when at one location to register with diierent positionsj picked up to render the control apparatus inopof a control member at the other location, checke erative, and means controlled by each return ing means partly at each 10Cati0n t0 Cause Said impulse received at said other locationl to reset Control apparatus t0 exchange between the tWe and initiate a new operation of each of said re'- locations check impulses to check the integrity lays, of said control apparatus, said checking means 18. In apparatus for eemmunieating between including a timing device leeated at Said Other two spaced locations over a single transmitting location and effective When Operated a Dredetercircuit, a .source of current of one frequency at mined time interval to initiate the sending of a one location and a. source of current of a second Cheek impulse and t0 maintain the Sending 0f frequency at the other location, receiving appasuch impulse until the receipt of a return check mtos4 at each location each coupled with said impulse from said one location, and means concircuit, the receiving apparatus at said one 10- trolled by each Such return impulse t0 initiate a cation responsive to current of said second freneW Operation 0f the timing device. and a delayed quency and the receiving apparatus at said other action' means associated With Said .timing device location responsive to current o! said one frequency, timing' means at said one location eifective when energized a. predetermined time interval to cause the associated source to 'supply current. to the transmitting circuit for iniluenction to cause said control apparatus to exchange between the two locations check impulses to check the integrity of said' control apparatus, said checking means including a ilrst and a second slow pickup relay and both of which are located at said other location, said ilrst relay having va relatively short pickup period and effective when picked up to initiate the sending has completed an operation to render the control apparatus inoperative. g

16. In apparatus for communicating between two spaced locations the combination comprising, control apparatus partly at each of said locations and effective to cause an operating mechanism at one location to register with different positions of a control member at the other location, checking means partly at each location to cause said control apparatus to exchange between the two locations check impulses to check the integrity of said control apparatus, said checking means including .a rst and a second timing de, vice and both of which devices are located at said other location, said ilrst timing device ef'- fective when operated a predetermined time interval to initiate the sending oi' a check impulse and to maintain the sending or such impulse until the receipt oi a return impulse from said one location, said second timing device eilfective when operated for a time interval .greater than said predetermined interval to'irender the control apparatus ineffective, and means controlled by each return impulse to initiate a new operation of each of said timing devices.

17. In apparatus for communicating between two spaced locations the combination comprising, control apparatus partly at each of said locations and eil'ective to cause an operating tion, ineans controlled by the receiving apparatus at said other location when inuenced to display a signal and to cause the associated source to supply current vto the circuit for iniluencing the receiving apparatus at said one location, and means controlled by the receiving apparatus at said one location when influenced to display a signal and to reset the timing means at its initial position.

19. Inapparatus for communicating between two spaced locations on a railway train the' combination comprising, transmitting and receiving tive to establish any one of several different operating conditions for the train at each of said locations, means to cause said apparatuses to exchange check impulsesbetween said locations and including a timing deviceat one location operable when energized a predetermined time interval to initiate the sending of a check impulse from said one location and to maintain the sending of such impulse until the receipt of a return check impulse from the other location, and'meansat said one location vcontrolled by each return check impulse to initiate energization of said timing device.

LELANDD.'

ferent positions of a control member at the other location, checking means partly at each locaing the receiving apparatus at said other loca-- apparatus at each of said locations and effec- 

